Rotating Ballnut - design ideas

[Boyan Silyavski]

Boyan, were you able to put some brain cells around the idea of keeping the same number of teeth, but lowering the overall height of the machined gear?

Mutzy

Yes, you made me do it

From table below we see that without changing anything, these 3 sized pulley will be possible to incorporate ion the rotating part without further change of components



So from these 3, it seems the best will be the P22-5M-15F . 22t is not so bad, outside diameter of the teeth is 35.01 so basically same as the 35mm of the OD of the part and the ID of the bearing. That will work.




Not to have in mind that 400w servos and bigger have shafts starting from 12 if not from 14mm in diameter. So smallest pulley there could be even the 12 teeth, also 14, 16, 18, 20. But in reality could be also 13, 15, 17, 19, as i can draw the pulley with as many teeth i would like to and it suits me.


from my Favourite belt calculator https://www.bbman.com/belt-length-calculator/ having in mind minimum distance from motor shaft to center of pulley is 90mm, and if bigger than 400W servo even 100mm, we could see that:

12t puley is No good, less than 6t engagement

But all puley more than 13t including are ok. Now it should be considered that the bending radius of 13t puley is too small, this for the durability of the belts. And believe me it will generate heat on the belt and pulley. But as belts is 3-4 $ its not of a great concern.


So yes, it could be done. 13t pulley and bigger.

now when you divide 22/13 , 22/14 etc. its not a whole number which i dont like. the first one that divides well is the 22/16=1.375 so nothing has to be rounded, 16t pulley i see as a minimum for a good bending radius. So that would be the one i would have used.


Obviously 2x 750W servos at both sides will do the job and if something extreme is desired even bigger could be fit. having in mind gantry around 180-250 kg and max machine speed at 30m/min with acceleration around 3000m/s2 which is my machine tested and it really rocks. You should do calculations again for the specific scenario but more or less thats it.
Also all time i am speaking of Samsung servos and brand servos in general. I have never tried the chinese servos but i think they will do well also. Plus really they are almost same price bigger or smaller/ servos must be correct size, not bigger or smaller /.

It should be noted that when i am engraving small stuff i lower the acceleration at 1000, talking about aluminum stamps and so. But this is very delicate work which normally is done on a mill.

I think that answers your question.

Boyan